Do not create Object Signing certificate

The Object Signing certificate created during server installation
was used only for signing the (recently removed) Firefox extension,
so there's no need to create that certificate any more.

Fixes: https://fedorahosted.org/freeipa/ticket/6399
Reviewed-By: Martin Basti <mbasti@redhat.com>
Reviewed-By: Jan Cholasta <jcholast@redhat.com>

install/ui/test/data/cert_find.json

@@ -57,15 +57,9 @@
                 "serial_number_hex": "0x9",
                 "status": "VALID",
                 "subject": "CN=dev.example.com,O=EXAMPLE.COM"
-            },
-            {
-                "serial_number": 10,
-                "serial_number_hex": "0xA",
-                "status": "VALID",
-                "subject": "CN=Object Signing Cert,O=EXAMPLE.COM"
             }
         ],
         "summary": "10 certificates matched",
         "truncated": false
     }
-}
+}